The present invention relates to chemical compounds that inhibit the mitotic checkpoint (also known as spindle checkpoint, spindle assembly checkpoint). The mitotic checkpoint is a surveillance mechanism that ensures proper chromosome segregation during mitosis. Every dividing cell has to ensure equal separation of the replicated chromosomes into the two daughter cells. Upon entry into mitosis, chromosomes are attached at their kinetochores to the microtubules of the spindle apparatus. The mitotic checkpoint is active as long as unattached kinetochores are present and prevents mitotic cells from entering anaphase and thereby completing cell division with unattached chromosomes [Suijkerbuijk and Kops, Biochemica et Biophysica Acta, 2008, 1786, 24-31; Musacchio and Salmon, Nat Rev Mol Cell Biol., 2007, 8, 379-93]. Lack of attachment results in the production of a molecular inhibitor of the anaphase promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase marking cyclin B and securin for proteasomal degradation [Pines J. Cubism and the cell cycle: the many faces of the APC/C. Nat. Rev. Mol. Cell Biol. 12, 427-438, 2012]. Once all kinetochores are attached in a correct amphitelic, i.e. bipolar, fashion with the mitotic spindle, the checkpoint is satisfied, APC/C gets active, and the cell enters anaphase and proceeds through mitosis. On a molecular basis the inhibitor of APC/C, the mitotic checkpoint complex (MCC) represents a complex of mitotic arrest deficient (Mad)-2, budding uninhibited by benzimidazole (Bub)-related-1 (BubR-1)/Mad-3, and Bub3 that directly binds and inactivates the essential APC/C stimulatory cofactor Cdc20. The protein kinase monopolar spindle-1 (Mps1) stimulates MCC assembly via Mad1 and, thus, represents the key activator of the spindle assembly checkpoint [recently reviewed in Vleugel at al. Evolution and function of the mitotic checkpoint. Dev. Cell 23, 239-250, 2012]. Furthermore, the protein kinase Bub1 contributes to APC/C inhibition by phosphorylation of Cdc20.
There is ample evidence linking reduced but incomplete mitotic checkpoint function with aneuploidy and tumorigenesis [Weaver and Cleveland, Cancer Research, 2007, 67, 10103-5; King, Biochimica et Biophysica Acta, 2008, 1786, 4-14]. In contrast, complete inhibition of the mitotic checkpoint, e.g. by knock-down of protein components of the checkpoint, has been recognised to result in severe chromosome missegregation and induction of apoptosis in tumour cells [Kops et al., Nature Reviews Cancer, 2005, 5, 773-85; Schmidt and Medema, Cell Cycle, 2006, 5, 159-63; Schmidt and Bastians, Drug Resistance Updates, 2007, 10, 162-81].
Interference with cell cycle regulation by chemical substances has long been recognized as a therapeutic strategy for the treatment of proliferative disorders including solid tumours such as carcinomas and sarcomas and leukaemias and lymphoid malignancies or other disorders associated with uncontrolled cellular proliferation. Classical approaches focus on the inhibition of mitotic progression (e.g. with antitubulin drugs, antimetabolites or CDK-inhibitors). Recently, a novel approach has gathered attention in inhibiting the mitotic checkpoint [Manchado et al., Cell Death and Differentiation, 2012, 19, 369-377; Colombo and Moll, Expert Opin. Ther. Targets, 2011, 15(5), 595-608; Janssen and Medema, Oncogene, 2011, 30(25), 2799-809]. Abrogation of the mitotic checkpoint is expected to increase erroneous chromosome segregation in cancer cells resulting in severe aneuploidy and cell death. Chemical inhibitors of Mps1 kinase activity have been published [Lan and Cleveland, J Cell Biol, 2010, 190, 21-24; Colombo et al., Cancer Res., 2010, 70, 10255-64; Tardif et al. Characterization of the cellular and antitumor effects of MPI-0479605, a small-molecule inhibitor of the mitotic kinase Mps1. Mol. Cancer Ther. 10, 2267-2275, 2011]. WO2011/063908 (Bayer Intellectual Property GmbH) relates to triazolopyridine compounds which are monopolar spindle 1 kinase (MPS-1 or UK) inhibitors. WO 2012/080230 (Bayer Intellectual Property GmbH) relates to substituted imidazopyrazine compounds which are monopolar spindle 1 kinase (MPS-1 or UK) inhibitors.
These Mps1-kinase directed compounds showed rapid inhibition of nocodazole-induced mitotic checkpoint activity, chromosome segregation defects and anti-proliferative activity in cellular assays, as well as tumor growth inhibitory effects in xenograft models.
The present invention relates to chemical compounds which inhibit the mitotic checkpoint in cellular assays without directly interfering with Mps1 kinase activity or with any other of the kinases reported of being involved in mitotic checkpoint such as Bub1, BubR1, Aurora A-C, or CDK1. Thus, the present invention discloses a novel approach for chemical intervention with mitotic checkpoint function.
WO 2011/003793 (BASF SE) relates to pyridazine compounds for controlling invertebrate pests, to a method for controlling invertebrate pests, to a method for protecting plant propagation material and/or the plants which grow therefrom, to plant propagation material, comprising at least one such compound, to a method for treating or protecting an animal from infestation or infection by parasites and to an agricultural composition containing at least one such compound.
WO 2002/068406 (Amgen Inc.) relates to substituted amine derivatives for the prophylaxis and treatment of diseases, such as angiogenesis mediated diseases.
However, the state of the art described above does not describe the specific substituted isothiazole compounds of general formula (I) of the present invention as defined herein, i.e. an isothiazole moiety, bearing:                in its 3-position, a C1-C3-alkyl-group, and        in its 4-position, a group of structure:        
wherein:                * indicates the point of attachment of said groups with the rest of the molecule, and        R2 represents phenyl or pyridinyl, which is optionally substituted as defined herein,and        in its 5-position, a group of structure:        
wherein:                * indicates the point of attachment of said groups with the rest of the molecule, and        A represents a heteroaryl group        
                wherein * indicates the point of attachment of said heteroaryl group, which is as defined herein and which is optionally substituted as defined herein;or a stereoisomer, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, or a mixture of same, as described and defined herein, and as hereinafter referred to as “compounds of the present invention”, or their pharmacological activity.        
It has now been found, and this constitutes the basis of the present invention, that said compounds of the present invention have surprising and advantageous properties.
In particular, said compounds of the present invention have surprisingly been found to effectively inhibit the spindle assembly checkpoint and may therefore be used for the treatment or prophylaxis of diseases of uncontrolled cell growth, proliferation and/or survival, inappropriate cellular immune responses, or inappropriate cellular inflammatory responses or diseases which are accompanied with uncontrolled cell growth, proliferation and/or survival, inappropriate cellular immune responses, or inappropriate cellular inflammatory responses, for example, haematological tumours, solid tumours, and/or metastases thereof, e.g. leukaemias and myelodysplastic syndrome, malignant lymphomas, head and neck tumours including brain tumours and brain metastases, tumours of the thorax including non-small cell and small cell lung tumours, gastrointestinal tumours, endocrine tumours, mammary and other gynaecological tumours, urological tumours including renal, bladder and prostate tumours, skin tumours, and sarcomas, and/or metastases thereof.